The present invention relates to a biopotential analysis system and method, and more particularly to a computer-based biopotential analysis system for determining, in a noninvasive manner, cerebral electrical properties.
Despite a considerable expenditure of time and effort, no approach for permitting quantitative, noninvasive assessments of cerebral electrical activity has been developed. A number of known devices are capable of providing a qualitative tracking of cerebral activity. Techniques such as the conventional EEG are restricted to analyses in the time domain. A more recent approach utilizes quantification of the frequency content of the EEG signal, as determined by the Fourier transform of the second order correlation function (better known as the power spectrum), but this technique has proven to be useful in only a limited number of situations.
The discharge of thousands of electrically active cells in the brain, organized in larger, interacting neural centers contributes to the formation of an extremely complicated, but well coordinated electrical signal. Embedded in that signal is information regarding frequency content, non-linearities, and phase relationships, all arising from the complex cerebral dynamics that take place. Because of the complexity of the EEG signal, conventional time and frequency modes of analysis are not particularly productive. The EEG is highly non-linear, and its intrinsic phase relationships must carry a great deal of information regarding cerebral function. Unfortunately, the power spectrum suppresses information regarding non-linearities and phase relationships and thus is of limited utility in extracting information available in the EEG.
The Fourier transform of the third order auto-correlation function, or bispectrum, is an analytic process that quantifies non-linearities and phase relationships intrinsic to any waveform. Although the application of bispectral analysis to EEG signals can be found in the prior art, it was only used as a test for demonstration purposes. The only known application was by T. P. Barnett and is described in Science 172:41-402 (1971), where bispectral analysis was applied to the EEG during various phases of sleep.
It is therefore a principal object of the present invention to provide a noninvasive system and method for diagnosing cerebral irregularities.
Another object of the present invention is to provide a system and method for noninvasively obtaining an intraoperative detection and quantification of cerebral ischemia.
A still further object of the present invention is to provide an apparatus and method for quantifying the adequacy of oxygenation of the critical region probed by a particular EEG lead.
A further object of the present invention is to provide a system and method for noninvasively quantifying the depth of anesthesia.
Yet another object of the present invention is to provide an apparatus and method for noninvasively quantifying the degree of intoxication.